1. Technical Field
The present disclosure relates to a fuel cell system capable of computing fuel level in a fuel tank, and more particularly to a fuel cell system capable of computing fuel level without using a flux sensor or flow rate sensor.
2. Discussion of Related Art
A fuel cell is a power generation system that directly converts energy from a chemical reaction, for example, between hydrogen and oxygen contained in organic substances, such as methanol, ethanol and natural gas, into electrical energy.
According to the type of electrolyte used, fuel cells can be sorted, for example, into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte fuel cell, and alkaline fuel cells. These respective fuel cells operate on the basic same principle, but differ in the types of fuels used, operating temperatures, catalyst, electrolytes, and the like.
Among the types, the polymer electrolyte membrane fuel cell (PEMFC) has advantages of remarkably high output, low driving temperature, and rapid start and response compared with other types of fuel cells, and can be widely applied as a mobile power source such as for portable electronic equipment or as a transportable power source such as a power source for an automobile as well as a distributed power source such as a stationary power plant used in a house and a public building, and the like.
A type of fuel cell is known as a direct methanol fuel cell (DMFC), which is similar to the polymer electrolyte membrane fuel cell but in which liquid methanol fuel is directly supplied to a stack. A DMFC includes, for example, a stack, a fuel tank, and a fuel pump. A hydrogen-containing fuel electrochemically reacts with an oxidant, such as oxygen, air, or the like, in the stack to generate electrical energy. Such a stack comprises several to several hundreds unit fuel cells, in which a membrane electrode assembly (MEA) and a separator are stacked. Herein, the membrane electrode assembly comprises an anode electrode (namely, “fuel electrode” or “oxidation electrode”) and a cathode electrode (namely, “air electrode” or “reduction electrode”) attached to each other, with a polymer electrolyte membrane disposed therebetween. The DMFC has a low operating temperature and can be miniaturized, and so is advantageous as a power supply for portable equipment such as notebook computers or portable game machines. However, when a fuel cell is used to power a notebook or similar device, unexpectedly running out of fuel during use is very undesirable. Therefore, a means for informing a user of the fuel level in the fuel tank, and in particular, a low fuel level, is useful.
Meanwhile, in the case of the DMFC, fuel may be supplied in exchangeable cartridges of predetermined size. In such an exchangeable cartridge system, informing a user that the fuel is almost depleted in the cartridge-in-use permits the user to exchange the cartridge for uninterrupted use of the device.
To this end, a flux meter is installed in the fuel tank or a sensing means such as a flux meter or a flow meter is installed in a fuel flow path from the fuel tank such that the residual or remaining fuel level in the fuel tank may be measured or computed. However, installing an extra flux meter or flow meter increases manufacturing costs as well, thereby complicating miniaturization or weight reduction of the fuel cell. Also, disposing a fuel sensing device in a disposable cartridge increases the cost of the cartridge.